1. Technical Field
The invention relates generally to a system for covering open top containers. More particularly, the invention relates to such a device which is mountable on a truck which includes an open top container. Specifically, the invention relates to such a device which utilizes a four-bar linkage in order to move a tarpaulin to cover the open top container.
2. Background Information
Large open containers are generally used for the purpose of transporting loose material, such as refuse, aggregates, construction debris or the like. In one application, these containers may be transported on large roll-off trucks, which allows for loading and unloading at different locations. These containers have an open top to allow for easy insertion of materials. Laws and regulations have been adopted in many areas specifying that these containers need to be covered during transit on public roadways to prevent material from being be blown out of the containers. Even where laws do not require this, it is beneficial to cover these containers in order to prevent damage to property from material that can be blown out during transport. These containers typically range in heights from 3 to 8 feet, and typically range in length from 14 to 24 feet. While it is possible to manually cover these containers, it is time consuming and expensive. The considerable variation in height and length of these containers complicate automatic tarping mechanisms.
Several inventions have been created to facilitate the automatic tarping of open top containers. One such device is depicted in U.S. Pat. No. 5,829,818. The device of the '818 patent provides two arms mounted with a cross beam and a spring-loaded roll of tarp material between one end of each arm and the other end of each arm pivotally affixed to the truck. The arms move through a fixed arc pulling a tarp over the top of the container as the arms move from the front to the rear of the container. The primary disadvantage of this invention is that it is difficult to accommodate various container sizes with the fixed length arms. Although, short containers could be covered by letting the tarp roller hang past the rear edge of the container, the dynamic loads on the overhanging weight could be damaging to the arms and pivots. Also, the weight of the arms and roller pulling the tarp over the rear edge of the container causes premature wear of the tarp material
Two approaches to create a covering device able to better adapt to various sized containers are shown in U.S. Pat. No. Re. 36,135 and U.S. Pat. No. 5,803,528. The invention of the '135 patent utilizes jointed arms, with a cylinder between the two arm sections. The base of each arm is mounted to the truck. The distal end of each arm supports the tarp roller. Actuating the cylinder between the two arm sections bends the arm at the joint, changing the distance between the base end and the tarp roller. The base arm is rotated by a cylinder attached to the truck on one end and the base arm on the other. The design of the '528 patent uses an actuated slider mechanism to vary the length of the tarp supporting arms. Both approaches offer effective methods of positioning the tarp at the rear edges of various container sizes. One of the disadvantages of both of the aforementioned systems relates to the initial movement of the tarp from its stowed position between the cab of the truck and the container. Most container tarpaulin systems store the cover or tarpaulin behind the cab of the truck and deploy the tarpaulin by raising it above the container on the truck frame and pulling the tarpaulin over the top of the container. It is desirable to have the tarp roller stored nearly at or below the height of the cab to lower wind resistance. Since many of the containers when sitting on the truck are substantially taller than the cab of the truck, the initial motion of the tarping mechanism must lift the tarp roller essentially straight up in between the cab and the front of the container in what is typically a narrow space. The converse is true when storing the tarp roller. If the initial motion is arcuate, the tarp roller will collide with either the cab or the container. Given that most tarpaulin systems or tarpers, including the aforementioned patented art, rotate or pivot, this straight line motion is only achieved by manipulating the arm length while simultaneously rotating the tarp carrying arms. Achieving the straight-line motion becomes a function of operator skill and often results in collisions between the tarper and the container, cab, or both.
Another disadvantage to U.S. Pat. No. 5,803,528 is that sliding motion is typically more expensive to fabricate and maintain. Grease is often used to facilitate sliding and is exposed on the extending part that the operator can touch. This can be a messy problem for the operator.
A further disadvantage with the aforementioned prior art is that a portion of the arm/arms of the tarping systems may extend above the top of the container for some or all container sizes when the tarp is deployed. This exposes the arms to damage from low tree limbs and the like. Additionally, the extending portion of the arms may pose a problem with regard to regulated height restrictions for the truck/container combinations when covering the tallest of typical containers.
A third approach taken to covering different sized open top containers is illustrated in U.S. Pat. No. 6,742,828. The '828 patent shows a device with two pivoted arm sections, which are controlled by actuators and sprockets. The first actuator controls the lower pivot arm, while a sprocket and gear assembly drives the upper pivot arm, which is controlled by a second actuator. This container covering device is comparatively complex and has a high part count. With an increase in complexity there is also an increase in cost of manufacturing and assembly. A further disadvantage of the '828 patent is that the lower arm section and upper arm section must stack laterally across the width of the truck. That is, the arms must be out of plane to avoid interference. In light of regulations governing the overall width of equipment such as tarpaulin systems or tarpers, an optimum design would minimize the width of the tarper mechanism and allow for the arms and its various sections to be in more or less the same plane. The stacking of the lower and upper arm in the '828 patent uses width that would ideally be used to provide clearance for the container or allow for wider containers to fit within the tarper system.
The purpose of the present invention is to provide a container covering device that addresses the deficiencies presented in the prior art.